Step 1Cut the onions in half from the stem top to the root bottom. Lay each half cut side down on a chopping board. Slice each half horizontally into 1/4-inch slices. Then cut down vertically into thin slices, and finish by cutting down crosswise so you have many small pieces of onion. Set aside.
Step 2Cut the garlic into thin slices lengthwise. Turn the slices on their side and cut into lengthwise thin slices. Holding the slices together, cut into small pieces vertically. Set aside with the onion.
Step 3Peel the potatoes and cut into 1-inch chunks. Add them to the onions and garlic.
Step 4Place the water and lentils into a pot. Add the onions, garlic, potatoes, sausage and salt and pepper to taste. Tear the bay leaf into several pieces and add to the pot. Bring to a simmer over medium heat. Cover, reduce the heat and simmer for 20 minutes.
Step 5Remove the lid and poke a piece of potato; if tender, fish out a little of the lentils and taste for tenderness. If both the potatoes and lentils are tender, they are ready to serve. If either is still firm, simmer another 10 minutes. Most of the liquid will have been absorbed. Serve in bowls.